A Rake's Progress

[delboy47]

I recently made a comment on a post on here regarding the amount of Kickback I was experiencing with my sliding compound mitre saw. Its an Evolution (I know!!!!)10 inch. Someone suggested I need a negative rake blade. I have looked at the original blade which seems to be zero rake angle but would be happy to try a new blade before parting company and getting an alternative saw.
However, I have been looking at a few crosscut blades (Freud, Erbauer etc) and their crosscut blades are showing a rake angle of the order of 13 to 15 degrees positive.
Confusion now reigns and I would welcome any help from you experienced guys. Is this correct for crosscut. Wires well and truly crossed now.

Thanks
Del

 

[Eric The Viking]

I had a conversation about this with Mr. Maskery (of this parish) recently, regarding my own mitre saw. Mine is using the blade it came with secondhand, which is a fine tooth Freud jobbie (250mm) that leaves an amazing finish, BUT has a slight positive rake.

Steve's point (will ask him to comment if he doesn't pick this up independently) was that the rake encourages the saw to grab and chuck stuff around. Negative rake pushes the stock into the fence and baseplate of the saw. Mine certainly does chuck small offcuts, but I persist in being contrary because of the quality of the cut from that blade. I've been suitably told off already!

It's better behaved cutting downwards than pushing away from me (I never pull it). I have never had actual kickback - it's usually a small loose piece at the end of a cut being flung. I treat it with care though: one side of the work is almost always clamped, and the other held in place with a push stick (there's no clamp on the right, nor any real way to make one fit). It's almost always crosscutting, apart from rare uses to trim small bits of ply, etc.

I'll probably try a negative rake blade when I come to replace the one I have though. The only thing that deters me is the finish quality. If you can get as good from a negative rake blade, it's a no-brainer.

Is the kickback possibly worse because of the way you're using it? I hesitate to ask, but I do get markedly different results depending on how I tackle a cut. have you experimented with different techniques - plunge versus pushing across, for example, and feed rates? Also (again I hesitate to ask) is the blade clean and reasonably sharp?

E.

 

[Steve Maskery]

A crosscut blade blade for a tablesaw will have a slightly positive rake (e.g.5°), but a crosscut blade for a SCMS will have a negative rake. Eric's reasons above are right. The force of the teeth pull the workpiece towards the centre of the blade. On a TS, this force is restrained by the surface of the table, but on a SCMS this same force is upwards. We don't want that, oh no, we don't want that.

 

[delboy47]

Gents
Thanks for your comments

Eric, the saw is quite new and not had a great deal of use so the blade should be OK. I have experimented with operation and tried pushme/pullyou etc but I have also had kickback when just using a chopping motion. Everything looks to be OK though and I can see no signs of any blade wobble etc.

Steve, you are of course quite correct, we don't want that!! I have become so wary of using it. My previous saw was a chopper (not sliding) and I never had a problem with that.

I will continue to look for a negative rake blade and try that as a first step. The second step should the problem persist will be bye bye saw and an alternative.

 

[SteveF]

when are you getting kickback...during the cut or straight afterwards?
I know my kapex will kick me if i lift after cut...wait for blade to stop first

Steve

 

[Steve Maskery]

Will this fit?

https://www.trenddirectuk.com/csb-cc250 ... oCIjbw_wcB

 

[delboy47]

Thanks again gents

SteveF - no I get it when cutting or chopping not just after the cut.

Steve M. Many thanks for that link. the shaft is 25.4 mm but I can get a reducer for that blade. I will be placing an order later today and give it a whirl. thanks a lot.

Del

Edit. Just seen that reducing bushes are included with the blade. Even better.

 

[Roughcut]

I have used an Evolution mitre saw (still on original blade) for maybe 4 years and haven't had a problem with kickback.
I always push the blade into the wood and waiting for the blade to stop spinning after a cut before lifting is always good practice .
Kickback can also be encountered on a work piece when the wood is clamped down both sides of the blade.

 

[delboy47]

Thanks for that Roughcut. Whatever happens I will "slow down" and wait on the blade stopping in future. every little helps. I only ever clamp one side.

 

[Adam9453]

What material are you cutting? Do you experience different results with different materials?
I saw someone recently getting severe kickback when using their SCMS to cut some tanalised 3x2 and when I stopped them (obviously to avoid an accident) it turned out the blade was 1 blunt and 2 not designed for cross cutting timber at all, he said he'd mainly used it for cutting metal and thought it was cutting "a bit funny"!! :shock:

 

[RobinBHM]

As above, a blunt blade is more likely to snatch, as is a rip saw blade in a chop saw.

A sharp positive blade will hardly cause any snatching, but the ideal blade will be a negative rake cutting blade, for the reasons Steve Maskery mentions and as he explained some cross cut blades will have a positive rake, as that is correct for a table saw.

Also how much gap do you have where the blade goes into the fence / swivel base plate. Some of these machines have quite a gap as a product of their big range of angles. If you are cutting small stuff all the same angle, a false bed and fence with a zero clearance will help.

 

[HOJ]

I would also check the back fences are aligned, I had a problem with my Kapex originally, till I made up a new fence which is straight.

 

[delboy47]

Thanks again for your comments Gents.
I will check out the things suggested but now intend changing the blade for a negative rake a la Steve Maskery's link.
The saw isn't very old and has not had a great deal of use so the blade should be fairly sharp. Used for a mixture of wood, probably predominantly softwood but some hard mainly oak. I have used it for a small amount of tanalised.
I will check gaps, rear fence etc as every little helps.
Much obliged to you all.
Del

 

[Eric The Viking]

... the blade should be fairly sharp. Used for a mixture of wood, probably predominantly softwood but some hard mainly oak. I have used it for a small amount of tanalised.

Make sure it's clean, too. I cut a lot of softwood, and the worst problem is baked-on resin, which scuffs in the cut causing scorch marks.Lots of people on here recommend using oven cleaner spray to clean blades. I've tried it and it works, but be sure you do it in a stainless sink (not ceramic), and rinse with a lot of running water, to avoid dissolving the pipework below (if that's plastic). Marigolds and green scouring pads shift it fast.

Beware though: I made the mistake of trying to rinse the blade off in the small sink in the downstairs loo - it barely fitted, I fumbled it, and I now have a chipped tooth or two (the sink itself seems to be fine). Was very easily done and the blade hardly touched the enamel - not dropped hard at all. It used to be a very nice, fine-toothed, Freud blade. Grrr!

I've also found xylene (from Toolstation), acetone and meths will help, none of which need more than newspaper and fresh air. I use a brass-bristled suede brush, as that survives most chemicals and can't hurt the blade.

E.

 

[Steve Maskery]

I clean mine in a melamine tray, the teeth are less prone to chipping. It's easily done though.
I use oven cleaner, or any kitchen cleaner I can find, TBH, and I show how I do it in my Tablesaw Basics DVD. However, since then, I've heard that oven cleaner is not the best as it can attack the bond between the WC and the steel plate of the blade. I don't know how true that is or to what extent it is a risk, but it is worth being aware of.